Device for eliminating short-circuits in erosion gap employed in transistortype generators designed for feeding electro-erosion machines



. E Ui@ 2m .70 8L PG PMN 3E... KM Pw AE ai GF wie NR wnun, oo VP ,IF n L gam AMES n wm S MMM Ecm l. MSD .uw m1 1v.. us UCWWS BmTIv. NCASl ROu ETERJ, RRNE 0E.d 01mm Ksmmm WYE ITM .Tum Mmm Is ,mn4 L WT Fm E c I .V E D ,2 m f if? Dec.130. 1969 United States Patent G U.s.s.R.

Fill-.angrily 3, 1961, ser. No. 651,000 i rm. ci. Hosb 37/03, 41/14 U.s. CIMM 2 claims ABsTlAcr oF THE DISCLOSURE A device is provided for eliminating short circuits in the erosion gapemployed in a transistor type generator designed for feeding erosion machines whereinfa low volitage D.C. powerl generator and an ignition direct voltage generator are connected to the erosion gap by means of transistor keys controlled by a master oscillator. The device includes a high resistance voltage transmitter connected to the erosion gp and to a two-stage amplifier provided with an integrating capacitor across the input and an actuating current control, the output of the amplifier being connected to a blocking generator which in turn is connected toda transistor key which is connected to the master oscillator input which is braked duringI a short circuit for substantial decrease of the erosion gap, at which time the blocking generator is self-oscillating.

This invention relatesfto a device for eliminating shortcircuits in the erosion gap employed in transistor-type generators designed for feeding electro-erosion iachines.

There are known transistor-type pulse generators of high efiiciency designed for feeding electrogerosion machines incorporating a low-voltage power generator synchronously operated with a low-capacity ignition pulse generator which provides for breakdown of the erosion gap at the required value of the operating clearance.

There are valso known devices employed, in the said generators and designed for avoiding overload of the lowvoltage power generator during short-circuiting in the erosion gap.

The device is fashioned as a transistor stage providedwith a transformer output, and an amplifier cutting off the transistor of the low-voltage power generator during short-circuiting.

The disadvantages of the known devices for eliminating short-circuits of this kind are as follows: incomplete switching-off of the transistor-type generator during shortcircuits, and .the impossibility to switch off the generator as the voltage drops across the erosion gap at the moments preceding the contact short-circuit.

An object of the present invention is to develop a device for eliminating short-circuits in the erosion gap and employed in a transistor-type generator designed for feeding electro-erosion machines, which provides for a complete disconnection of the transistor-type generator during short-circuiting or substantial decrease of the erosion gap.

Another object of the invention is to develop a device for eliminating short-circuits in the erosion gap, which provides for easy connection of the transistor-type generator after elimination of the short-circuit.

The aforementioned and other objects of the invention are achieved in a device for eliminating short circuits in the erosion gap employed in a transistor-type generator designed for feeding erosion machines wherein a'lowvoltage D.C. power generator and an ignition directs volt- Patented Dec. 30, 1969 fzice age generator are connected to the erosion gap by means of transistor keys controlled by a master oscillator which is adapted for producing oscillations of a given frequency when excited, which device, according to the invention, comprises a high-resistance voltage transmitter connected to the erosion gap and coupled to a two-stage amplifier provided with an integrating capacitor across the input and an actuating current control, a blocking-generator connected to the latter amplifiers output and a transistor key connected to the master oscillator input and braking it during a short-circuit or substantial decrease of the erosion gap.

It is expedient to employ as the high-resistance voltage transmitter on the`erosion gap, resistors shunting the transistor cascades connected in series in the ignition voltage circuit and protecting the transistors against overvoltages.

Other objects and advantages of the present invention will become apparent from the description of an embodiment thereof and the accompanying drawings, wherein:

FIG. l illustrates the electrical circuit diagram of the transistor-type generator, according to the invention; and

FIG. 2 shows the electrical circuit diagram of the device for eliminating short-circuits with the blocking-generator of the master oscillator, according to the invention.

The transistor-type generator designed for feeding electro-erosion machines comprises a low-capacity ignition pulse generator and a low-voltage power generator.

The low-capacity ignition pulse generator constitutes a direct ignition voltage source 1 to be connected to the erosion gap 2 through stages 3 employing transistors 4 and connected in series since the value of ignition pulse (-300 v.) is substantially higher than that of the maximum permissible voltage of collector-emitter of the transistors employed. Witlithe electrodes separated, the ignition pulse circuit is closed through a resistor 5 connected in parallel to the erosion gap 2. Resistors 6 shunting the transistor stages 3 connected in series and preventing the transistors 4 against overvoltages along with the resistor 5 and the direct voltage voltage source 1 from a highresistance Voltage tran'smmitter on the erosion gap 2.

The low-voltage power generator constitutes a lowvoltage D.C. source 7 connected to the erosion gap through parallel transistor stages 8 employing transistors 9 and a separating power diode 10. The transistors 4 and 9 operate in the mode of CUTOFF-SATURATION, i.e. in the key mode. -B'oth generators are actuated syn-` chronously by the master oscillator 11 wherein pulse repetition frequency can be controlled, for example, by a base resistor 12 (FIG. 2) of a blocking-generator 13.

The transistor-type generator is provided with a device for eliminating short-circuits which constitutes a twostage amplifier 14 employing transistors 15 and 16 with an integrating capacitor on the input and an actuating current control on the resistors 18 and 19, a blockinggenerator 20 employing a transistor 21 and connected to the collector of the transistor 16 through a diode 22 and a transistor key 23, whose input is connected to an output winding 24 of a transformer 25 and a capacitor 26. The collector of a transistor 27 of the key 23 is connected through a diode 28 to the common point of base resistors 29, 30 of the blocking-generator 13 of the master oscillator 11.

The transistor-type generator operates as follows:

Pulse voltage of the low-capacity ignition pulse generator initiates the discharge, for which purpose a pulse amplitude of current 0.5-3 a. is quite sufficient. After'breakdown of the erosion gap 2, the separator diode 10 be-k comes conductive and a power pulse of the current amplitude of tens-hundreds amperes is shaped from the low-voltage power generator which performs follow-up.

3 Since the value of the average voltage across the erosion gap as the operating pulse is supplied thereto is equal to 18-35 v. depending on the electrode material and the interelectrode medium, the voltage of the power generator is to be selected as equal to 40-60 v.

The device for eliminating short-circuits operates as follows:

Voltage is supplied from the erosion gap 2 through the resistors 18, 31 to the input of the transistor 15. The ratio between the cutolf base current of the transistor and the voltage across the erosion gap 2, and between the enabling current and the collector voltage Ek source, is controlled by the resistors 18 and 19. As the operating clearance is substantially decreased preceding the shortcircuit, the voltage across the erosion gap drops down so that the transistor 15 becomes conductive, while the transistor 16 is cutoff, as a result, the diode 22 becomes inhibited, and the blocking-generator 20 starts operating in the mode of auto-oscillations. `In this case, the pulse voltage generated across the output winding 24 of the transformer 25 is integrated on the capacitor 26 and enables the transistor 27 up to saturation. The blockinggenerator 13 of the master oscillator 11 is braked through the diode 28. After elimination of the short-circuit the capacitor 17 across the input of the transistor 15 is recharged by means of an operating feed controller (not shown in the drawing). As the transistor 15 gets cutoff, the transistor 16 becomes conductive up to saturation. In this case, the diode 22 becomes conductive and the blocking-generator 20 is braked, i.e. the transistor 27 of the 156.3 23 is cutoff, thus cutting off the diode 22. The master oscillator resumes operation.

The described device ensures operation of the transistor-type generator as it is disconnected during a shortcircuit or substantial decrease of the erosion gap and connected after elimination of the short-circuit.

When operating the present device, the power transistors are protected against current overloads, thus preventv ing the wire-electrodes against breaks during cutting-out operations and against electrode lsticking during broachn'g operations.

Though the present invention has been described in connection with a preferred embodiment thereof, various alterations and modifications may take place without departing from the spirit and scope of the invention, as those skilled in the art will easily understand,

We claim:

1. In a transistor-type generatorvfor feeding electroerosion machines, comprising: a low-voltage D.C. power supply source connected to the erosion gap; an ignition direct voltage source connected tol the erosion gap in parallel-to the said low-voltage power source; transistor keys arranged in the circuit of the said sources and connecting synchronously the said sources to the erosion gap; a master oscillator connected to the said transistor keys for producing oscillations of a given frequency, and means for eliminating short-circuits in the erosion gap, which comprises: a high-resistance voltage transmitter connected to the erosion gap; a two-stage amplifier provided with an integrating capacitor on the input and with an actuating current control and connected to the said high-resistance voltage transmitter; a blocking-generator connected to the output of the said two-stage amplifier and adapted for undergoing auto-oscillation when said gap is `short circuited or substantially decreased; and a transistor key connected with its input to the said blocking-generator, and with its output to the input of the said master oscillator and braking the latter during short-cir cuiting or substantial decrease of the erosion gap when the blocking-generator is oscillating.

2. A device, according to claim 1, wherein said high resistance voltage transmitter on Vthe erosion gap comprises resistors shunting the transistor stages connected in series in the circuit of the said direct voltage ignition source and protecting the transistors of the said stages against overvoltages.

References Cited UNITED STATES PATENTS 3,257,580 6/1966 Webb. 3,267,327 8/1966 Webb. 3,228,635 6/1967 Webb.

JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner U.S. Cl. XR. 

